Curable composition for lens, lens and optical device

ABSTRACT

Provided is a curable composition capable of giving a lens that has excellent transfer accuracy from a mold and offers heat resistance and optical properties at excellent levels. The curable composition according to the present invention for lens formation contains a cycloaliphatic epoxide (A) represented by Formula (a), a cationic-polymerization initiator (B), and a polysiloxane (C) represented by Formula (c). The curable composition contains the polysiloxane (C) in an amount of 0.01% to 5% by weight based on the total amount of the curable composition. The curable composition according to the present invention for lens formation may further contain a siloxane compound (D) containing two or more epoxy groups per molecule.

TECHNICAL FIELD

The present invention relates to a curable composition for lensformation, which is a curable composition suitable for lens productionusing a mold; to a lens obtained by curing the curable composition forlens formation; and to an optical device including the lens. Thisapplication claims priority to Japanese Patent Application No.2013-269397 filed to Japan Dec. 26, 2013, and to Japanese PatentApplication No. 2014-221123 filed to Japan Oct. 30, 2014, the entirecontents of which are incorporated herein by reference.

BACKGROUND ART

Electronic products undergo significant reduction in size and weight andextraordinary increase in performance. Such electronic products arerepresented typically by cellular phones, smartphones, tablet terminals,mobile computers, personal digital assistants (PDAs), and digital stillcameras (DSCs). With the technological trend as above, demands areincreasingly made to achieve reduction in size, weight, and/or thicknessof lenses for use typically in cameras to be mounted to the electronicproducts.

The lenses are generally produced by a molding (forming) technique usinga mold, such as injection molding or cast molding. Known materials foruse in lens formation include thermoplastic resins such aspolycarbonates; and thermal- or photo-curable resins such as acrylicresins and silicone resins (Patent Literature (PTL) 1 to 4). However,the thermoplastic resins do not have reflow heat resistance, and, forexample, camera modules using lenses made from the thermoplastic resinsshould be assembled in a step different from other parts, and thisdisadvantageously complicates the production process. In contrast,lenses made from acrylic resins or silicone resins are superior in heatresistance, but are not yet satisfactory in optical properties.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication (JP-A) No.2005-119124

PTL 2: Japanese Patent No. 4800383

PTL 3: Japanese Patent No. 4124991

PTL 4: JP-A No. H11-092539

SUMMARY OF INVENTION Technical Problem

The inventors of the present invention found that a cationically curablecompound containing a cycloaliphatic epoxy group, when used, gives alens having heat resistance and optical properties both at excellentlevels. However, the inventors also found as follows. When wafer-levellenses and other lenses reduced in size, weight, and/or thickness, andFresnel lenses and other specially-shaped lenses are produced using amold, “bubble entrapment” often occurs upon charging of a curablecomposition containing the cationically curable compound into the mold,and the “bubble entrapment” impairs transfer accuracy from the mold.

Accordingly, the present invention has an object to provide a curablecomposition capable of forming a lens that has excellent transferaccuracy from the mold and offers heat resistance and optical propertiesat excellent levels.

The present invention has another object to provide a lens and a methodfor producing the lens, where the lens has excellent transfer accuracyfrom the mold and offers heat resistance and optical properties atexcellent levels.

The present invention has yet another object to provide an opticaldevice including the lens.

Solution to Problem

After intensive investigations to achieve the objects, the inventorshave found that a curable composition including a specific epoxide and aspecific polysiloxane can have better wettability with a mold, and thiseliminates or minimizes the occurrence of “bubble entrapment” uponcharging of the curable composition into the mold; and that the curablecomposition has excellent curability and gives a lens having heatresistance, optical properties, and transfer accuracy from the mold atexcellent levels. The present invention has been made based on thesefindings.

Specifically, the present invention provides a curable composition forlens formation, including a cycloaliphatic epoxide (A) represented byFormula (a), a cationic-polymerization initiator (B), and a polysiloxane(C) represented by Formula (c). The curable composition contains thepolysiloxane (C) in a content of 0.01% to 5% by weight based on thetotal amount (100% by weight) of the curable composition. Formulae (a)and (c) are expressed as follows:

where R¹ to R¹⁸ are each, identically or differently, selected fromhydrogen, halogen, a hydrocarbon group which may contain oxygen orhalogen, and optionally substituted alkoxy; X is selected from a singlebond and a linkage group excluding a siloxane-bond-containing group,

where R¹⁹ to R²² each represent, identically or differently in eachoccurrence, a group selected from hydrogen, alkyl, haloalkyl, aryl,aralkyl, alkoxy, acyloxy, and —RNHCOR′, where R is selected fromalkylene and alkenylene, and R′ is selected from alkyl and alkenyl; andm and n each represent, identically or differently, an integer of 1 ormore.

The curable composition for lens formation may further include asiloxane compound (D) containing two or more epoxy groups per molecule.

The curable composition for lens formation may further include acationically curable compound containing one or more oxetane groups permolecule, excluding compounds belonging to the cycloaliphatic epoxide(A) and the siloxane compound (D).

The curable composition for lens formation may further include acationically curable compound containing one or more glycidyl ethergroups per molecule, excluding compounds belonging to the cycloaliphaticepoxide (A) and the siloxane compound (D).

The curable composition for lens formation may contain thecycloaliphatic epoxide (A) in a content of 5% to 60% by weight based onthe total amount (100% by weight) of the curable composition.

The curable composition for lens formation may be used to form awafer-level lens.

The curable composition for lens formation may be used to form a Fresnellens.

The curable composition for lens formation may be used to form a lensfor camera flash.

The present invention also provides a method for producing a lens, wherethe method includes steps 1 and 2 as follows. In the step 1, the curablecomposition for lens formation is charged into a lens-forming mold. Inthe step 2, light is applied to the curable composition to cure thecurable composition.

In the lens production method, a silicon mold may be used as thelens-forming mold.

In the step 2 in the lens production method, light at 350 to 450 nm maybe applied from a UV-LED to cure the curable composition.

In the step 2 in the lens production method may further includeannealing after the light application.

In the step 1 in the lens production method, a lens-forming mold havingtwo or more lens patterns may be used as the lens-forming mold.

In the lens production method, the lens may be obtained by using alens-forming mold having two or more lens patterns as the lens-formingmold in the step 1, subjecting an article obtained from the step 1 tothe step 2 to give a coupled lens assembly including two or more lensescoupled to each other, and cutting the coupled lens assembly.

The present invention also provides a lens that is obtained by the lensproduction method and includes two or more lenses coupled to each other.

The present invention also provides a lens obtained by the lensproduction method.

The lens may be a wafer-level lens.

The lens may be a Fresnel lens.

The lens may be a lens for camera flash.

In addition and advantageously, the present invention provides anoptical device including the lens.

Specifically, the present invention relates to followings.

(1) The present invention relates to a curable composition for lensformation. The curable composition contains a cycloaliphatic epoxide (A)represented by Formula (a), a cationic-polymerization initiator (B), anda polysiloxane (C) represented by Formula (c). The curable compositionfor lens formation contains the polysiloxane (C) in a content of 0.01%to 5% by weight based on the total amount (100% by weight) of thecurable composition.

(2) The curable composition according to (1) for lens formation mayfurther include a siloxane compound (D) containing two or more epoxygroups per molecule.

(3) The curable composition according to one of (1) and (2) for lensformation may further include a cationically curable compound containingone or more oxetane groups per molecule (excluding compounds belongingto the cycloaliphatic epoxide (A) and the siloxane compound (D)).

(4) The curable composition according to any one of (1) to (3) for lensformation may further include a cationically curable compound containingone or more glycidyl ether groups per molecule (excluding compoundsbelonging to the cycloaliphatic epoxide (A) and the siloxane compound(D)).

(5) The curable composition according to any one of (1) to (4) for lensformation may contain the cycloaliphatic epoxide (A) in a content of 5%to 60% by weight based on the total amount (100% by weight) of thecurable composition for lens formation.

(6) The cycloaliphatic epoxide (A) in the curable composition accordingto any one of (1) to (5) for lens formation may be at least one compoundselected from the group consisting of (3,4,3′,4′-diepoxy)bicyclohexyl,bis(3,4-epoxycyclohexylmethyl) ether, and2,2-bis(3,4-epoxycyclohex-1-yl)propane.

(7) The curable composition according to any one of (1) to (6) for lensformation may contain the cycloaliphatic epoxide (A) in an amount of 10%to 50% by weight based on the total amount (100% by weight) of allcationically curable compounds contained in the curable composition forlens formation.

(8) The cationic-polymerization initiator (B) in the curable compositionaccording to any one of (1) to (7) for lens formation may be a sulfoniumsalt compound.

(9) The cationic-polymerization initiator (B) in the curable compositionaccording to any one of (1) to (8) for lens formation may contain anarylsulfonium ion as a cationic moiety.

(10) The curable composition according to any one of (1) to (9) for lensformation may contain the cationic-polymerization initiator (B) in anamount of 0.01 to 15 parts by weight per 100 parts by weight of allcationically curable compounds contained in the curable composition forlens formation.

(11) The curable composition according to any one of (1) to (10) forlens formation may contain the polysiloxane (C) in an amount of 0.01 to5 parts by weight per 100 parts by weight of all cationically curablecompounds contained in the curable composition for lens formation.

(12) The siloxane compound (D) in the curable composition according toany one of (2) to (11) for lens formation may be a compound representedby Formula (d).

(13) The siloxane compound (D) in the curable composition according toany one of (2) to (11) for lens formation may be at least one selectedfrom the group consisting of compounds represented by Formulae (d-1) to(d-7).

(14) The curable composition according to any one of (2) to (13) forlens formation may contain the siloxane compound (D) in a content of 1%to 60% by weight based on the total amount (100% by weight) of thecurable composition for lens formation.

(15) The curable composition according to any one of (1) to (14) forlens formation may further contain at least one of a hydrogenatedglycidyl ether epoxide and an oxetane compound in an amount of 5% to 60%by weight based on the total amount (100% by weight) of all cationicallycurable compounds contained in the curable composition for lensformation.

(16) The curable composition according to any one of (1) to (15) forlens formation may further contain a hydrogenated glycidyl ether epoxidein an amount of 5% to 60% by weight based on the total amount (100% byweight) of all cationically curable compounds contained in the curablecomposition for lens formation.

(17) The curable composition according to any one of (1) to (16) forlens formation may further contain an oxetane compound in an amount of5% to 30% by weight based on the total amount (100% by weight) of allcationically curable compounds contained in the curable composition forlens formation.

(18) The curable composition according to any one of (1) to (17) forlens formation may have a viscosity of 2000 mPa·s or less at atemperature of 25° C. and a rotation speed of 20 revolutions per second.

(19) The curable composition according to any one of (1) to (18) forlens formation may have a contact angle of 50° or less with respect to asilicon substrate, where the contact angle is determined by a sessiledrop method.

(20) The curable composition according to any one of (1) to (19) forlens formation may be used to form a wafer-level lens.

(21) The curable composition according to any one of (1) to (19) forlens formation may be used to form a Fresnel lens.

(22) The curable composition according to any one of (1) to (19) forlens formation may be used to form a lens for camera flash.

(23) The present invention also relates to a cured product of thecurable composition according to any one of (1) to (22) for lensformation.

(24) The cured product according to (23) may have a transmittance of 70%or more at 400 nm in terms of 0.5 mm thickness.

(25) The cured product according to one of (23) and (24) may have aglass transition temperature (Tg) of 100° C. or higher.

(26) The cured product according to any one of (23) to (25) may have alinear expansion coefficient α1 of 40 to 100 ppm/° C. at temperaturesequal to or lower than the glass transition temperature and a linearexpansion coefficient α2 of 90 to 150 ppm/° C. at temperatures equal toor higher than the glass transition temperature.

(27) The cured product according to any one of (23) to (26) may have astorage modulus of 0.1 GPa or more at 25° C.

(28) The present invention also relates to a lens including the curedproduct according to any one of (23) to (27).

(29) The present invention also relates to a method for producing alens. The method includes the steps 1 and 2 as follows. In the step 1,the curable composition according to any one of (1) to (22) for lensformation is charged into a lens-forming mold. In the step 2, light isapplied to cure the curable composition.

(30) The lens production method according to (29) may use a silicon moldas the lens-forming mold.

(31) The step 2 in the lens production method according to one of (29)and (30) may include applying light at 350 to 450 nm from a UV-LED tocure the curable composition.

(32) The step 2 in the lens production method according to any one of(29) to (31) may further include annealing after the light application.

(33) In the step 1 in the lens production method according to any one of(29) to (32), a lens-forming mold having two or more lens patterns maybe used as the lens-forming mold.

(34) The lens production method according to any one of (29) to (32) maybe performed by using a lens-forming mold having two or more lenspatterns as the lens-forming mold in the step 1, subjecting an articlefrom the step 1 to the step 2 to give a coupled lens assembly includingtwo or more lenses coupled to each other, and cutting the obtainedcoupled lens assembly to give lenses.

(35) The present invention also relates to a lens produced by the lensproduction method according to (33) and including two or more lensescoupled to each other.

(36) The present invention also relates to a lens produced by the lensproduction method according to any one of (29) to (34).

(37) The lens according to one of (35) and (36) may be a wafer-levellens.

(38) The lens according to one of (35) and (36) may be a Fresnel lens.

(39) The lens according to one of (35) and (36) may be a lens for cameraflash.

(40) In addition and advantageously, the present invention relates to anoptical device including the lens according to any one of (35) to (39).

Advantageous Effects of Invention

The curable composition according to the present invention for lensformation, as having the configuration, has better wettability with amold, and this eliminates or minimizes the occurrence of “bubbleentrapment” upon charging of the curable composition into the mold. Inaddition, the curable composition has excellent curability and can forma cured product having heat resistance and optical properties (such astransparency, high refractive index, and yellowing resistance) atexcellent levels. Thus, the use of the curable composition according tothe present invention for lens formation gives a lens that has excellenttransfer accuracy from the mold and offers heat resistance and opticalproperties at excellent levels. The curable composition is thereforeadvantageously usable for the production of wafer-level lenses and otherlenses reduced in size, weight, and/or thickness; and Fresnel lenses andother specially-shaped lenses, where the production is performed using amold.

The lens according to the present invention is made from (derived from)the curable composition for lens formation as a material and thereby hasexcellent transfer accuracy from the mold and offers heat resistance andoptical properties at excellent levels.

The optical device according to the present invention has high qualitybecause of including the lens having excellent transfer accuracy fromthe mold and offering heat resistance and optical properties atexcellent levels.

As used herein the term “wafer-level lens” refers to a lens for use inwafer-level production of a camera to be used typically in a cellularphone. A single wafer-level lens has dimensions of a diameter of about 1to about 10 mm and a thickness of about 100 to about 2000 μm.

The term “Fresnel lens” refers to a lens that is designed by dividing aregular lens into a set of concentric annular sections and has a smallerthickness as compared with the regular lens. The Fresnel lens has aridged (sawtooth) cross sections. A single Fresnel lens has dimensionsof a diameter of about 1 to about 10 mm and a thickness of about 100 toabout 2000 μm.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) and 1(b) are a schematic cross-sectional view and d schematictop view, respectively, of a Fresnel lens.

DESCRIPTION OF EMBODIMENTS

Curable Composition for Lens Formation

The curable composition according to the present invention for lensformation is hereinafter also simply referred to as a “curablecomposition”. The curable composition contains a cycloaliphatic epoxide(A), a cationic-polymerization initiator (B), and a polysiloxane (C).The curable composition contains the polysiloxane (C) in an amount of0.01% to 5% by weight based on the total amount (100% by weight) of thecurable composition.

Cycloaliphatic Epoxide (A)

The cycloaliphatic epoxide (A) as an essential component of the curablecomposition according to the present invention is a cationically curablecompound represented by Formula (a). However, the term “cycloaliphaticepoxide (A)” excludes siloxane-bond-containing compounds. Formula (a) isexpressed as follows:

In Formula (a), R¹ to R¹⁸ are each, identically or differently, selectedfrom hydrogen, halogen, a hydrocarbon group which may contain oxygen orhalogen, and optionally substituted alkoxy.

Non-limiting examples of the halogen as R¹ to R¹⁸ include fluorine,chlorine, bromine, and iodine.

Examples of the hydrocarbon group as R¹ to R¹⁸ include aliphatichydrocarbon groups, alicyclic hydrocarbon groups, aromatic hydrocarbongroups, and groups including two or more of them bonded to each other.

Non-limiting examples of the aliphatic hydrocarbon groups include C₁-C₂₀alkyl such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl,isooctyl, decyl, and dodecyl, of which C₁-C₁₀ alkyl is preferred, andC₁-C₄ alkyl is particularly preferred; C₂-C₂₀ alkenyl such as vinyl,allyl, methallyl, 1-propenyl, isopropenyl, 1-butenyl, 2-butenyl,3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, and5-hexenyl, of which C₂-C₁₀ alkenyl is preferred, and C₂-C₄ alkenyl isparticularly preferred; and C₂-C₂₀ alkynyl such as ethynyl and propynyl,of which C₂-C₁₀ alkynyl is preferred, and C₂-C₄ alkynyl is particularlypreferred.

Non-limiting examples of the alicyclic hydrocarbon groups include C₃-C₁₂cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, andcyclododecyl; C₃-C₁₂ cycloalkenyl such as cyclohexenyl; and C₄-C₁₅bridged hydrocarbon groups such as bicycloheptyl and bicycloheptenyl.

Non-limiting examples of the aromatic hydrocarbon groups include C₆-C₁₄aryl such as phenyl and naphthyl, of which C₆-C₁₀ aryl is preferred.

Non-limiting examples of the groups including two or more groupsselected from the aliphatic hydrocarbon groups, the alicyclichydrocarbon groups, and the aromatic hydrocarbon groups include C₃-C₁₂cycloalkyl-substituted C₁-C₂₀ alkyl such as cyclohexylmethyl; C₁-C₂₀alkyl-substituted C₃-C₁₂ cycloalkyl such as methylcyclohexyl; C₇-C₁₈aralkyl such as benzyl and phenethyl, of which C₇-C₁₀ aralkyl istypified; C₆-C₁₄ aryl-substituted C₂-C₂₀ alkenyl such as cinnamyl;C₁-C₂₀ alkyl-substituted C₆-C₁₄ aryl such as tolyl; and C₂-C₂₀alkenyl-substituted C₆-C₁₄ aryl such as styryl.

Non-limiting examples of the hydrocarbon group which may contain oxygenor halogen, as R¹ to R¹⁸, include groups corresponding to thehydrocarbon groups, except with an oxygen-containing group and/or ahalogen atom replacing at least one hydrogen atom. Non-limiting examplesof the oxygen-containing group include hydroxy; hydroperoxy; C₁-C₁₀alkoxy such as methoxy, ethoxy, propoxy, isopropyloxy, butoxy, andisobutyloxy; alkenyloxy such as allyloxy; tolyloxy, naphthyloxy, andother C₆-C₁₄ aryloxy which may be substituted with one or moresubstituents selected from the group consisting of C₁-C₁₀ alkyl, C₂-C₁₀alkenyl, halogen, and C₁-C₁₀ alkoxy; C₇-C₁₈ aralkyloxy such as benzyloxyand phenethyloxy; C₁-C₁₀ acyloxy such as acetyloxy, propionyloxy,(meth)acryloyloxy, and benzoyloxy; C₁-C₁₀ alkoxycarbonyl such asmethoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and butoxycarbonyl;and phenoxycarbonyl, tolyloxycarbonyl, naphthyloxycarbonyl and otherC₆-C₁₄ aryloxycarbonyl which may be substituted with one or moresubstituents selected from the group consisting of C₁-C₁₀ alkyl, C₂-C₁₀alkenyl, halogen, and C₁-C₁₀ alkoxy; C₇-C₁₈ aralkyloxycarbonyl such asbenzyloxycarbonyl; epoxy-containing groups such as glycidyloxy;oxetanyl-containing groups such as ethyloxetanyloxy; C₁-C₁₀ acyl such asacetyl, propionyl, and benzoyl; isocyanato; sulfo; carbamoyl; oxo; andgroups including two or more of these groups bonded to each other withor without the medium typically of C₁-C₁₀ alkylene.

Examples of the alkoxy as R¹ to R¹⁸ include C₁-C₁₀ alkoxy such asmethoxy, ethoxy, propoxy, isopropyloxy, butoxy, and isobutyloxy.

Non-limiting examples of the substituents which the alkoxy may haveinclude halogen, hydroxy, C₁-C₁₀ alkoxy, C₂-C₁₀ alkenyloxy, C₆-C₁₄aryloxy, C₁-C₁₀ acyloxy, mercapto, alkylthio, C₂-C₁₀ alkenylthio, C₆-C₁₄arylthio, C₇-C₁₈ aralkylthio, carboxy, alkoxy-carbonyl, C₆-C₁₄aryloxy-carbonyl, C₇-C₁₈ aralkyloxy-carbonyl, amino, mono- or di-(C₁-C₁₀alkyl)amino, acylamino, epoxy-containing groups, oxetanyl-containinggroups, C₁-C₁₀ acyl, oxo, and groups including two or more of thesegroups bonded to each other with or without the medium typically ofC₁-C₁₀ alkylene.

In Formula (a), X is selected from a single bond and a linkage group.The “linkage group” refers to a divalent group containing one or moreatoms, but excludes siloxane-bond-containing groups. Non-limitingexamples of the linkage group include divalent hydrocarbon groups,carbonyl, ether bond, ester bond, carbonate, amido, and groups includingtwo or more of these groups coupled to each other.

The divalent hydrocarbon groups include C₁-C₁₈ straight or branchedchain alkylene and divalent alicyclic hydrocarbon groups. Non-limitingexamples of the C₁-C₁₀ straight or branched chain alkylene includemethylene, methylmethylene, dimethylmethylene, ethylene, propylene, andtrimethylene. Non-limiting examples of the divalent alicyclichydrocarbon groups include cycloalkylene (including cycloalkylidene),such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene,1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, andcyclohexylidene.

In particular, the linkage group as X is preferably selected fromoxygen-containing linkage groups such as —CO—, —O—CO—O—, —COO—, —O—,—CONH—; groups including two or more of these groups coupled to eachother; and groups including one or more of these groups coupled to oneor more of the divalent hydrocarbon groups.

Representative examples of the cycloaliphatic epoxide represented byFormula (a) include, but are not limited to,(3,4,3′,4′-diepoxy)bicyclohexyl, bis(3,4-epoxycyclohexylmethyl) ether,1,2-epoxy-1,2-bis(3,4-epoxycyclohex-1-yl)ethane,2,2-bis(3,4-epoxycyclohex-1-yl)propane,1,2-bis(3,4-epoxycyclohex-1-yl)ethane, and compounds exemplified byFormulae (a-1) to (a-10) below. In Formulae (a-5) and (a-7), n¹ and n²each independently represent an integer of 1 to 30. L in Formula (a-5)represents, independently in each occurrence, C₁-C₈ alkylene and isexemplified by straight or branched chain alkylene such as methylene,ethylene, propylene, isopropylene, butylene, isobutylene, s-butylene,pentylene, hexylene, heptylene, and octylene. Among them, L ispreferably selected from C₁-C₃ straight or branched chain alkylene suchas methylene, ethylene, propylene, and isopropylene. In Formulae (a-9)and (a-10), n³ to n⁸ each represent, identically or differently, aninteger of 1 to 30.

The curable composition according to the present invention may containeach of different cycloaliphatic epoxides (A) alone or in combination.The cycloaliphatic epoxides (A) may be produced by known or commonmethods.

In particular, the curable composition preferably contains, as thecycloaliphatic epoxide (A), at least one selected from the groupconsisting of (3,4,3′,4′-diepoxy)bicyclohexyl,bis(3,4-epoxycyclohexylmethyl) ether, and2,2-bis(3,4-epoxycyclohex-1-yl)propane, as an essential component. Thisis preferred because the curable composition has excellent curabilityand can give a cured product that has excellent properties such as heatresistance, optical properties, moisture resistance, low shrinkage, andlow linear expansion.

The curable composition according to the present invention may containthe cycloaliphatic epoxide (A) in a content (blending amount) ofpreferably 5% to 60% by weight, more preferably 10% to 55% by weight,and furthermore preferably 15% to 50% by weight, based on the totalamount (100% by weight) of the curable composition. The curablecomposition, if containing the cycloaliphatic epoxide (A) in a contentout of the range, may hardly allow the cured product to have heatresistance and mechanical strength both at high levels.

The curable composition may contain the cycloaliphatic epoxide (A) in acontent (blending amount) of preferably 10% to 50% by weight, morepreferably 15% to 45% by weight, and furthermore preferably 20% to 40%by weight, based on the total amount (100% by weight) of allcationically curable compounds (the total amount of all cationicallycurable compounds such as epoxides and oxetane compounds) contained inthe curable composition. The curable composition, if containing thecycloaliphatic epoxide (A) in a content less than the range, may haveinsufficient curability and may cause the cured product to beinsufficient in properties such as moisture resistance, heat resistance(glass transition temperature), low shrinkage, and low linear expansion,in some usage modes. In contrast, the curable composition, if containingthe cycloaliphatic epoxide (A) in a content greater than the range, maycause the cured product to have insufficient mechanical strength.

Cationic-Polymerization Initiator (B)

The cationic-polymerization initiator for use in the present inventionmay be selected from a cationic photoinitiator and a cationic thermalinitiator.

The “cationic photoinitiator” refers to a compound that generates acationic species via light application to initiate a curing reaction ofa cationically curable compound. The cationic photoinitiator includes acationic moiety and an anionic moiety, where the cationic moiety absorbsthe light, and the anionic moiety serves as an acid source.

Non-limiting examples of the cationic photoinitiator include diazoniumsalt compounds, iodonium salt compounds, sulfonium salt compounds,phosphonium salt compounds, selenium salt compounds, oxonium saltcompounds, ammonium salt compounds, and bromine salt compounds. Amongthem, the cationic photoinitiator for use in the present invention ispreferably selected from sulfonium salt compounds. This is preferred forthe formation of a cured product with excellent curability.

Non-limiting examples of the cationic moiety in the sulfonium saltcompounds include arylsulfonium ions such as triphenylsulfonium ion,diphenyl[4-(phenylthio)phenyl]sulfonium ion, tri-p-tolylsulfonium ion,(4-hydroxyphenyl)methylbenzylsulfonium ion, and4-(4-biphenylylthio)phenyl-4-biphenylylphenylsulfonium ion, of whichtriarylsulfonium ions are typified.

Non-limiting examples of the anionic moiety include[(Y)_(s)B(Phf)_(4-s)]⁻, where Y is selected from phenyl and biphenylyl,Phf represents phenyl with at least one selected from the groupconsisting of perfluoroalkyl, perfluoroalkoxy, and halogen replacing atleast one of hydrogen atoms, and s is an integer of 0 to 3; BF₄ ⁻;[(Rf)_(n)PF_(6-n)]⁻, where Rf represents alkyl with fluorine atomsreplacing 80% or more of hydrogen atoms, and n is an integer of 0 to 5;AsF₆ ⁻, SbF₆ ⁻, and pentafluorohydroxyantimonate.

Non-limiting examples of the cationic photoinitiator for use in thepresent invention include (4-hydroxyphenyl)methylbenzylsulfoniumtetrakis(pentafluorophenyl)borate,4-(4-biphenylylthio)phenyl-4-biphenylylphenylsulfoniumtetrakis(pentafluorophenyl)borate, 4-(phenylthio)phenyldiphenylsulfoniumphenyltris(pentafluorophenyl)borate,[4-(4-biphenylylthio)phenyl]-4-biphenylylphenylsulfoniumphenyltris(pentafluorophenyl)borate,diphenyl[4-(phenylthio)phenyl]sulfoniumtris(pentafluoroethyl)trifluorophosphate,diphenyl[4-(phenylthio)phenyl]sulfoniumtetrakis(pentafluorophenyl)borate,diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate,4-(4-biphenylylthio)phenyl-4-biphenylylphenylsulfoniumtris(pentafluoroethyl)trifluorophosphate,bis[4-(diphenylsulfonio)phenyl]sulfidephenyltris(pentafluorophenyl)borate,[4-(2-thioxanthonylthio)phenyl]phenyl-2-thioxanthonylsulfoniumphenyltris(pentafluorophenyl)borate,4-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate, as well ascommercial products available typically under trade names CYRACUREUVI-6970, CYRACURE UVI-6974, CYRACURE UVI-6990, and CYRACURE UVI-950(each supplied by Union Carbide Corporation, U.S.A.), IRGACURE 250,IRGACURE 261, IRGACURE 264 (each supplied by Ciba Specialty ChemicalsCorporation), SP-150, SP-151, SP-170, and OPTOMER SP-171 (each suppliedby ADEKA CORPORATION), CG-24-61 (supplied by Ciba Specialty ChemicalsCorporation), DAICAT II (supplied by Daicel Corporation), UVAC1590 andUVAC1591 (each supplied by DAICEL-CYTEC Company, Ltd.), CI-2064,CI-2639, CI-2624, CI-2481, CI-2734, CI-2855, CI-2823, CI-2758, andCIT-1682 (each supplied by Nippon Soda Co., Ltd.), PI-2074 (supplied byRhodia, (toluylcumyl)iodonium tetrakis(pentafluorophenyl)borate), FFC509(supplied by 3M Corporation), BBI-102, BBI-101, BBI-103, MPI-103,TPS-103, MDS-103, DTS-103, NAT-103, and NDS-103 (each supplied by MidoriKagaku Co., Ltd.), CD-1010, CD-1011, and CD-1012 (each supplied bySartomer Company, Inc., U.S.A.), CPI-100P, CPI-101A, and CPI-200K (eachsupplied by San-Apro Ltd.).

The “cationic thermal initiator” refers to a compound that generates acationic species upon the application of heat to initiate a curingreaction of a cationically curable compound. The cationic thermalinitiator includes a cationic moiety and an anionic moiety, where thecationic moiety absorbs heat, and the anionic moiety serves as an acidsource.

Non-limiting examples of the cationic thermal initiator for use in thepresent invention include iodonium salt compounds and sulfonium saltcompounds.

Non-limiting examples of the cationic moiety in the cationic thermalinitiator include arylsulfonium ions such as4-hydroxyphenyl-methyl-benzylsulfonium ion,4-hydroxyphenyl-methyl-(2-methylbenzyl)sulfonium ion,4-hydroxyphenyl-methyl-1-naphthylmethylsulfonium ion, andp-methoxycarbonyloxyphenyl-benzyl-methylsulfonium ion, of whichmonoarylsulfonium ions are typified.

The anionic moiety in the cationic thermal initiator is exemplified aswith the anionic moiety in the cationic photoinitiator.

Non-limiting examples of the cationic thermal initiator include4-hydroxyphenyl-methyl-benzylsulfoniumphenyltris(pentafluorophenyl)borate,4-hydroxyphenyl-methyl-(2-methylbenzyl)sulfoniumphenyltris(pentafluorophenyl)borate,4-hydroxyphenyl-methyl-1-naphthylmethylsulfoniumphenyltris(pentafluorophenyl)borate, andp-methoxycarbonyloxyphenyl-benzyl-methylsulfoniumphenyltris(pentafluorophenyl)borate.

The curable composition may contain each of differentcationic-polymerization initiators alone or in combination. The curablecomposition may contain the cationic-polymerization initiator(s) in anamount (blending amount) of preferably 0.01 to 15 parts by weight, morepreferably 0.01 to 10 parts by weight, furthermore preferably 0.05 to 10parts by weight, and particularly preferably 0.1 to 5 parts by weight,per 100 parts by weight of the total amount of all cationically curablecompounds (the total amount of cationically curable compounds such asepoxides and oxetane compounds) contained in the curable composition.The curable composition, when containing the cationic-polymerizationinitiator(s) in an amount within the range, gives a cured product havingproperties such as heat resistance and optical properties at excellentlevels.

Polysiloxane (C)

The polysiloxane for use in the present invention is a compoundrepresented by Formula (c) and has excellent leveling properties. Thepresence of the polysiloxane in the curable composition according to thepresent invention allows the curable composition to have betterwettability with a mold and eliminates or minimizes the occurrence of“bubble entrapment” upon charging of the curable composition into themold, without affecting curability of cationically curable compoundscontained in the curable composition. The curable composition maycontain each of different polysiloxanes alone or in combination. Formula(c) is expressed as follows:

In Formula (c), R¹⁹ to R²² each represent, identically or differently ineach occurrence, a group selected from hydrogen, alkyl, haloalkyl, aryl,aralkyl, alkoxy, acyloxy, and —RNHCOR′, where R is selected fromalkylene and alkenylene, and R′ is selected from alkyl and alkenyl.

Non-limiting examples of the alkyl as R¹⁹ to R²² include C₁-C₂₀ alkylsuch as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, isooctyl,decyl, and dodecyl, of which C₁-C₁₀ alkyl is preferred, and C₁-C₄ alkylis particularly preferred.

Non-limiting examples of the haloalkyl as R¹⁹ to R²² includechloromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, pentafluoroethyl,3,3,3-trifluoropropyl, and other groups corresponding to the alkylexemplified as the alkyl as R¹⁹ to R²², except with one or more halogenatoms replacing hydrogen atoms.

Non-limiting examples of the aryl as R¹⁹ to R²² include C₆-C₁₄ aryl suchas phenyl and naphthyl, of which C₆-C₁₀ aryl is preferred.

Non-limiting examples of the aralkyl as R¹⁹ to R²² include C₇-C₁₈aralkyl such as benzyl and phenethyl, of which C₇-C₁₀ aralkyl ispreferred.

Non-limiting examples of the alkoxy as R¹⁹ to R²² include C₁-C₁₀ alkoxysuch as methoxy, ethoxy, propoxy, isopropyloxy, butoxy, and isobutyloxy.

Non-limiting examples of the acyloxy as R¹⁹ to R²² include C₁-C₁₀acyloxy such as acetyloxy, propionyloxy, (meth)acryloyloxy, andbenzoyloxy.

R in the —RNHCOR′ group is selected from alkylene and alkenylene and isexemplified by, but not limited to, straight or branched chain C₁-C₁₂alkylene such as methylene, ethylene, methylethylene, trimethylene,1-methyltrimethylene, 2-methyltrimethylene, 2,2-dimethyltrimethylene,tetramethylene, pentamethylene, hexamethylene, heptamethylene,octamethylene, nonamethylene, 2,2,4-trimethylhexamethylene,decamethylene, and dodecamethylene; and straight or branched chain C₂-C₃alkenylene such as vinylene and propenylene.

R′ in the —RNHCOR′ group is selected from alkyl and alkenyl and isexemplified by, but not limited to, C₁-C₂₀ alkyl such as methyl, ethyl,propyl, isopropyl, butyl, hexyl, octyl, isooctyl, decyl, and dodecyl;and C₂-C₂₀ alkenyl such as vinyl, allyl, methallyl, 1-propenyl,isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl,3-pentenyl, 4-pentenyl, and 5-hexenyl.

In Formula (c), m and n each represent, identically or differently, aninteger of 1 or more (e.g., an integer of 1 to 500).

The polysiloxane for use in the present invention may be selected fromcommercial products available typically under trade names BYK-UV3510 andBYK-307 (each supplied by BYK Japan KK), and trade name DISPARLON 1930N(supplied by Kusumoto Chemicals, Ltd.).

The curable composition contains the polysiloxane in a content of 0.01%to 5% by weight based on the total amount (100% by weight) of thecurable composition. The content is preferably 0.05% to 4% by weight,and particularly preferably 0.1% to 3% by weight. The curablecomposition may contain the polysiloxane in a proportion of typically0.01 to 5 parts by weight, preferably 0.05 to 4 parts by weight, andparticularly preferably 0.1 to 3 parts by weight, per 100 parts byweight of all cationically curable compounds (the total amount of allcationically curable compounds such as epoxides and oxetane compounds)contained in the curable composition. The presence of the polysiloxanein a content (proportion) within the range allows the curablecomposition to have better wettability with a mold and eliminates orminimizes the occurrence of “bubble entrapment” upon charging of thecurable composition into the mold.

Siloxane Compound (D)

The curable composition according to the present invention preferablyfurther contains a siloxane compound (D) as a cationically curablecompound in addition to the cycloaliphatic epoxide (A). The “siloxanecompound (D)” refers to a compound having two or more epoxy groups permolecule and further having a siloxane skeleton including siloxane bond(Si—O—Si). The siloxane skeleton may be selected from cyclic siloxaneskeletons, straight or branched chain silicones (straight chain orbranched chain polysiloxanes), and cage-like or ladder-likepolysilsesquioxanes. In particular, the siloxane compound (D) for use inthe present invention is preferably a compound having a cyclic siloxaneskeleton, because this configuration allows the curable composition tohave excellent curability and to give a lens that has heat resistanceand mechanical strength at excellent levels. Namely, the siloxanecompound (D) is preferably a cyclic siloxane containing two or moreepoxy groups per molecule.

When the siloxane compound (D) is a cyclic siloxane containing two ormore epoxy groups, the number of Si—O units constituting the siloxanering is preferably 2 to 12, and more preferably 4 to 8. This ispreferred for the curable composition to have excellent curability andto give a lens that has heat resistance and mechanical strength atexcellent levels. The number of Si—O units is equal to the number ofsilicon atoms constituting the siloxane ring.

The number of epoxy groups per molecule of the siloxane compound (D) isnot limited, as long as being 2 or more, but preferably 2 to 4, and morepreferably 3 or 4. This is preferred for the curable composition to haveexcellent curability and to give a lens that has heat resistance andmechanical strength at excellent levels.

The siloxane compound (D) has an epoxy equivalent (weight per epoxyequivalent) of preferably 150 to 400, more preferably 180 to 350, andfurthermore preferably 180 to 300. This is preferred for the curablecomposition to have excellent curability and to give a lens that hasheat resistance and mechanical strength at excellent levels. The epoxyequivalent is determined in conformity with JIS K 7236.

At least one of the epoxy groups in the siloxane compound (D) ispreferably a cycloaliphatic epoxy group and is more preferably acyclohexene oxide group. This is preferred for the curable compositionto have excellent curability and to give a lens that has heat resistanceand mechanical strength at excellent levels. The “cycloaliphatic epoxygroup” refers to an epoxy group including an oxygen atom bonded in atriangular arrangement to two adjacent carbon atoms constituting analiphatic ring. The “cyclohexene oxide group” refers to an epoxy groupincluding an oxygen atom bonded in a triangular arrangement to twoadjacent carbon atoms constituting a cyclohexane ring.

Non-limiting examples of the siloxane compound (D) include compounds(cyclic siloxanes) represented by Formula (d):

In Formula (d), R²³ and R²⁴ each represent, identically or differentlyin each occurrence, selected from a cycloaliphatic-epoxy-containingmonovalent group and alkyl, where at least two of “k” occurrences of R²³and “k” occurrences of R²⁴ in the compound represented by Formula (d)are each independently a cycloaliphatic-epoxy-containing monovalentgroup. The number k in Formula (d) represents an integer of 3 or more(and is preferably an integer of 3 to 6). The “k” occurrences of R²³ andthe “k” occurrences of R²⁴ in the compound represented by Formula (d)may be identical or different.

A non-limiting examples of the cycloaliphatic-epoxy-containingmonovalent group as R²³ and R²⁴ is -A-R²⁵, where “A” representsalkylene; and R²⁵ represents a cycloaliphatic epoxy group. Non-limitingexamples of the alkylene as “A” include C₁-C₁₈ straight or branchedchain alkylene such as methylene, methylmethylene, dimethylmethylene,ethylene, propylene, and trimethylene. A non-limiting example of thegroup R²⁵ is a cyclohexene oxide group.

Non-limiting examples of the alkyl as R²³ and R²⁴ include C₁-C₁₂straight or branched chain alkyl.

Specifically, non-limiting examples of the siloxane compound (D) include2,4-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,6,8,8-hexamethyl-cyclotetrasiloxane,4,8-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,2,4,6,6,8-hexamethyl-cyclotetrasiloxane,2,4-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-6,8-dipropyl-2,4,6,8-tetramethyl-cyclotetrasiloxane,4,8-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,6-dipropyl-2,4,6,8-tetramethyl-cyclotetrasiloxane,2,4,8-tri[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,6,8-pentamethyl-cyclotetrasiloxane,2,4,8-tri[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-6-propyl-2,4,6,8-tetramethyl-cyclotetrasiloxane,2,4,6,8-tetra[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,8-tetramethyl-cyclotetrasiloxane,and epoxy-containing silsesquioxanes.

More specifically, non-limiting examples of the siloxane compound (D)include compounds represented by Formulae (d-1) to (d-7):

The siloxane compound (D) may also be selected from thecycloaliphatic-epoxy-containing silicone resins described in JP-A No.2008-248169; and the organopolysilsesquioxane resins containing at leasttwo epoxy functional groups per molecule, described in JP-A No.2008-19422.

The curable composition according to the present invention may containeach of different siloxane compounds (D) alone or in combination. Suchsiloxane compounds (D) may also be selected from commercial productsavailable typically under trade names X-40-2678, X-40-2670, andX-40-2720 (each supplied by Shin-Etsu Chemical Co., Ltd.).

The curable composition according to the present invention may containthe siloxane compound (D) in a content (blending amount) of preferably1% to 50% by weight, more preferably 5% to 45% by weight, andfurthermore preferably 10% to 40% by weight, based on the total amount(100% by weight) of the curable composition.

The curable composition according to the present invention may containthe siloxane compound (D) in a proportion (blending amount) ofpreferably 1% to 60% by weight, more preferably 5% to 55% by weight, andfurthermore preferably 10% to 50% by weight, based on the total amount(100% by weight) of all cationically curable compounds (the total amountof all cationically curable compounds such as epoxides and oxetanecompounds) contained in the curable composition. The curablecomposition, when containing the siloxane compound (D) in a content(proportion) within the range, effectively allows the resulting lens tohave heat resistance and mechanical strength at higher levels.

Other Cationically Curable Compound (E)

The curable composition according to the present invention may furthercontain one or more other cationically curable compounds. The term“other cationically curable compound” refers to a cationically curablecompound excluding the cycloaliphatic epoxides (A) and the siloxanecompounds (D).

Non-limiting examples of the other cationically curable compoundsinclude other epoxides; oxetane compounds; and vinyl ether compounds.The term “other epoxide” refers to a compound that contains one or moreepoxy groups per molecule, but excludes the cycloaliphatic epoxides (A)and the siloxane compounds (D). The term “oxetane compound” refers to acompound that contains one or more oxetane groups per molecule. The term“vinyl ether compound” refers to a compound that contains one or morevinyl ether groups per molecule. The presence of the other cationicallycurable compound(s) may allow the curable composition according to thepresent invention to be controlled in viscosity so as to have betterhandleability and/or to less shrink upon curing in lens formation.

The other epoxides are exemplified by, but not limited to, compoundscontaining one or more glycidyl ether groups per molecule. Non-limitingexamples of the compounds containing one or more glycidyl ether groupsper molecule include aromatic glycidyl ether epoxides such asbisphenol-A epoxides, bisphenol-F epoxides, biphenol epoxides, phenolnovolac epoxides, cresol novolac epoxides, cresol novolac epoxides ofbisphenol-A, naphthalene epoxides, and epoxides derived fromtrisphenolmethane; hydrogenated glycidyl ether epoxides; glycidyl esterepoxides; and glycidylamine epoxides.

Non-limiting examples of the hydrogenated glycidyl ether epoxidesinclude hydrogenated bisphenol-A epoxides (compounds derived frombisphenol-A epoxides via hydrogenation) such as2,2-bis[4-(2,3-epoxypropoxy)cyclohexyl]propane,2,2-bis[3,5-dimethyl-4-(2,3-epoxypropoxy)cyclohexyl]propane, andmultimers of them; hydrogenated bisphenol-F epoxides (compounds derivedfrom bisphenol-F epoxides via hydrogenation) such asbis[o,o-(2,3-epoxypropoxy)cyclohexyl]methane,bis[o,p-(2,3-epoxypropoxy)cyclohexyl]methane,bis[p,p-(2,3-epoxypropoxy)cyclohexyl]methane,bis[3,5-dimethyl-4-(2,3-epoxypropoxy)cyclohexyl]methane, and multimersof them; hydrogenated biphenol epoxides; hydrogenated phenol novolacepoxides; hydrogenated cresol novolac epoxides; hydrogenated cresolnovolac epoxides of bisphenol-A; hydrogenated naphthalene epoxides; andhydrogenated products of epoxides derived from trisphenolmethane.Commercial products available typically under trade name YX8000(supplied by Mitsubishi Chemical Corporation) may be used herein.

Examples of the other epoxides also include compounds each containing anepoxy group directly bonded to an alicycle, such as a compoundrepresented by Formula (e-1):

In Formula (e-1), R²⁶ represents a group corresponding to a “q”-hydricalcohol, except for removing —OH in the number of “q”; and p and q eachindependently represent a natural number. Non-limiting examples of the“q”-hydric alcohol (R²⁶—(OH)_(q)) include2,2-bis(hydroxymethyl)-1-butanol and other polyhydric alcohols, of whichC₁-C₁₅ alcohols are typified. The number q is preferably from 1 to 6,and the number p is preferably from 1 to 30. When q is 2 or more, two ormore occurrences of p in two or more occurrences of the group in theparentheses (round brackets) may be identical or different.Specifically, non-limiting examples of the compound include1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of2,2-bis(hydroxymethyl)-1-butanol, trade name EHPE3150 (supplied byDaicel Corporation).

Non-limiting examples of the oxetane compounds include trimethyleneoxide, 3,3-bis(vinyloxymethyl)oxetane, 3-ethyl-3-hydroxymethyloxetane,3-ethyl-3-(2-ethylhexyloxymethyl)oxetane,3-ethyl-3-(hydroxymethyl)oxetane, 3-ethyl-3-[(phenoxy)methyl]oxetane,3-ethyl-3-(hexyloxymethyl)oxetane, 3-ethyl-3-(chloromethyl)oxetane,3,3-bis(chloromethyl)oxetane,1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, bis{[1-ethyl(3-oxetanyl)]methyl} ether,4,4′-bis[(3-ethyl-3-oxetanyl)methoxymethyl]bicyclohexyl,1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]cyclohexane, and3-ethyl-3-{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane. Commercialproducts available typically under trade names ARON OXETANE OXT221 andARON OXETANE OXT101 (each supplied by Toagosei Co., Ltd.) may be used.

Non-limiting examples of the vinyl ether compounds include2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropylvinyl ether, 2-hydroxyisopropyl vinyl ether, 4-hydroxybutyl vinyl ether,3-hydroxybutyl vinyl ether, 2-hydroxybutyl vinyl ether,3-hydroxyisobutyl vinyl ether, 2-hydroxyisobutyl vinyl ether,1-methyl-3-hydroxypropyl vinyl ether, 1-methyl-2-hydroxypropyl vinylether, 1-hydroxymethylpropyl vinyl ether, 4-hydroxycyclohexyl vinylether, 1,6-hexanediol monovinyl ether, 1,4-cyclohexanedimethanolmonovinyl ether, 1,3-cyclohexanedimethanol monovinyl ether,1,2-cyclohexanedimethanol monovinyl ether, p-xylene glycol monovinylether, m-xylene glycol monovinyl ether, o-xylene glycol monovinyl ether,diethylene glycol monovinyl ether, triethylene glycol monovinyl ether,tetraethylene glycol monovinyl ether, pentaethylene glycol monovinylether, oligo(ethylene glycol) monovinyl ethers, poly(ethylene glycol)monovinyl ethers, dipropylene glycol monovinyl ether, tripropyleneglycol monovinyl ether, tetrapropylene glycol monovinyl ether,pentapropylene glycol monovinyl ether, oligo(propylene glycol) monovinylethers, poly(propylene glycol) monovinyl ethers, and derivatives ofthem.

In particular, the other cationically curable compound (E) for use inthe present invention is preferably at least one selected from thecompounds containing one or more glycidyl ether groups per molecule (ofwhich the hydrogenated glycidyl ether epoxides are more preferred) andthe oxetane compounds.

The curable composition may contain the other cationically curablecompound in a content (blending amount) of typically about 5% to about60% by weight, preferably 10% to 60% by weight, and particularlypreferably 20% to 50% by weight, based on the total amount (100% byweight) of the curable composition. When the curable compositioncontains two or more different other cationically curable compounds, theterm “content” refers to the total content of them. The curablecomposition may contain the other cationically curable compound in aproportion (blending amount) of typically about 5% to about 60% byweight, preferably 10% to 60% by weight, and particularly preferably 20%to 50% by weight, based on the total amount (100% by weight) of allcationically curable compounds (the total amount of all cationicallycurable compounds such as epoxides and oxetane compounds) contained inthe curable composition. When the curable composition contains two ormore different other cationically curable compounds, the term“proportion” refers to the total proportion of them.

In an embodiment of the present invention, the curable compositionpreferably contains, as the other cationically curable compound, acompound containing one or more glycidyl ether groups per molecule (ofwhich a hydrogenated glycidyl ether epoxide is more preferred). This ispreferred for the curable composition to give a lens having still bettermechanical strength. The curable composition preferably contains thecompound containing one or more glycidyl ether groups per molecule (inparticular, the hydrogenated glycidyl ether epoxide) in an amount oftypically about 5% to about 60% by weight, more preferably 10% to 60% byweight, and particularly preferably 20% to 50% by weight, based on thetotal amount (100% by weight) of all cationically curable compounds (thetotal amount of all cationically curable compounds such as epoxides andoxetane compounds) contained in the curable composition.

In another embodiment of the present invention, the curable compositionpreferably contains, as the other cationically curable compound, anoxetane compound. This is preferred for the curable composition to havebetter curability (in particular, curability upon curing via ultravioletirradiation). The curable composition preferably contains the oxetanecompound in an amount of typically about 5% to about 30% by weight, morepreferably 5% to 25% by weight, and particularly preferably 10% to 20%by weight, based on the total amount (100% by weight) of allcationically curable compounds (the total amount of all cationicallycurable compounds such as epoxides and oxetane compounds) contained inthe curable composition.

Additives

The curable composition according to the present invention may furthercontain one or more other additives, in addition to the compounds. Theadditives may be selected from known or common additives and areexemplified by, but are not limited to, solvents, metal oxide particles,rubber particles, silicone- or fluorine-containing antifoaming agents,silane coupling agents, fillers, plasticizers, leveling agents excludingthe polysiloxanes (C), antistatic agents, flame retardants, colorants,antioxidants, ultraviolet absorbers, ion adsorbents, pigments, and moldrelease agents. The content (blending amount) of these additives ispreferably set to 5% by weight or less based on the total amount (100%by weight) of the curable composition. The curable composition accordingto the present invention may contain a solvent, but the amount of thesolvent is preferably controlled to 10% by weight or less, and morepreferably 1% by weight or less, based on the total amount (100% byweight) of the curable composition. This is because the curablecomposition, if containing an excessively large amount of the solvent,may cause the lens to include bubbles.

The colorants (or coloring matter) include pigments and dyes. Thecurable composition may contain each of different colorants alone or incombination.

Non-limiting examples of the pigments include inorganic pigments such ascarbon black, chromium oxide, iron oxide, black titanium oxide,acetylene black, lamps black, bone black, graphite, iron black,copper-chromium black pigments, copper-iron-manganese black pigments,cobalt-iron-chromium black pigments, ruthenium oxide, graphite, fineparticles of metals (e.g., aluminum), fine metal oxide particles, finecomplex oxide particles, fine metal sulfide particles, and fine metalnitride particles; organic pigments such as perylene black, cyanineblack, aniline black, azo pigments, anthraquinone pigments,isoindolinone pigments, indanthrene pigments, indigo pigments,quinacridone pigments, dioxazine pigments, tetraazaporphyrin pigments,triarylmethane pigments, phthalocyanine pigments, perylene pigments,benzimidazolone pigments, and rhodamine pigments; and pigments derivedfrom inorganic pigments, except for being coated with organic materialssuch as resins.

Non-limiting examples of the dyes include azo dyes; anthraquinone dyessuch as acid violet 39, acid violet 41, acid violet 42, acid violet 43,acid violet 48, acid violet 51, acid violet 34, acid violet 47, acidviolet 109, acid violet 126, basic violet 24, basic violet 25, disperseviolet 1, disperse violet 4, disperse violet 26, disperse violet 27,disperse violet 28, disperse violet 57, solvent violet 11, solventviolet 13, solvent violet 14, solvent violet 26, solvent violet 28,solvent violet 31, solvent violet 36, solvent violet 37, solvent violet38, solvent violet 48, solvent violet 59, solvent violet 60, vat violet13, vat violet 15, and vat violet 16; indigo dyes; carbonyl dyes;xanthene dyes; quinoneimine dyes; quinoline dyes; tetraazaporphyrindyes; triarylmethane dyes; naphthoquinone dyes; nitro dyes;phthalocyanine dyes; fluoran dyes; perylene dyes; methine dyes; andrhodamine dyes.

The content of the colorant in the curable composition according to thepresent invention for lens formation may be adjusted as appropriateaccording to the intended use and is typically about 10 to 300 ppm basedon the total amount of the curable composition for lens formation. Thelower limit of the content is preferably 50 ppm, and particularlypreferably 100 ppm. When the curable composition contains two or moredifferent colorants, the term “content” refers to the total content ofthem.

The curable composition according to the present invention may beprepared typically by blending predetermined amounts of thecycloaliphatic epoxide (A), the cationic-polymerization initiator (B),and the polysiloxane (C), and optional components added as needed, suchas the siloxane compound (D), the other cationically curable compound(E), and the additives, and mixing and stirring these components, wherenecessary with debubbling under vacuum. The stirring/mixing ispreferably performed at a temperature of about 10° C. to about 60° C.The stirring/mixing may be performed using a known or common device.Such devices are exemplified by planetary centrifugal mixers, single- ormulti-screw extruders, planetary mixers, kneaders, and dissolvers.

The curable composition according to the present invention has aviscosity of preferably 2000 mPa·s or less, more preferably 1000 mPa·sor less, and furthermore preferably 500 mPa·s or less, at a temperatureof 25° C. and a rotation speed of 20 revolutions per second. Control ofthe viscosity of the curable composition according to the presentinvention within the range allows the curable composition to have betterfluidity, to less suffer from remaining of bubbles, and to be chargedinto the lens-forming mold while restraining increase of injectionpressure. Specifically, the control allows the curable compositionaccording to the present invention to have better coatability and betterchargeability and to offer better workability over the entire moldingoperation of the curable composition.

The curable composition according to the present invention has excellentwettability with a mold and has a contact angle of typically 50° orless, preferably 40° or less, particularly preferably less than 40°, andmost preferably 35° or less, with a flat silicon substrate. Thisconfiguration eliminates or minimizes the occurrence of “bubbleentrapment” upon charging of the curable composition into the mold. Thecontact angle of the curable composition may be measured by a sessiledrop method and, more specifically, may be measured by the methoddescribed in working examples.

In addition, the curable composition according to the present inventionhas excellent curability and, by ultraviolet irradiation, forms a curedproduct having properties as mentioned below. This makes the curablecomposition advantageously usable as a material typically forwafer-level lenses, Fresnel lenses, lenses for camera flash, and anyother lenses.

The cured product of the curable composition according to the presentinvention is hereinafter also referred to as a “cured product accordingto the present invention”. The cured product according to the presentinvention has excellenL mechanical strength and still maintains a highglass transition temperature. The curing of the curable compositionaccording to the present invention may be allowed to proceed typicallyby the method described in after-mentioned “lens production method”.

The cured product according to the present invention has a transmittance(in terms of 0.5 mm thickness) of preferably 70% or more (e.g., 70% to100%), more preferably 75% or more, furthermore preferably 80% or more,and particularly preferably 85% or more at 400 nm.

The cured product according to the present invention has a refractiveindex of preferably 1.40 to 1.60, and more preferably 1.48 to 1.58.

The cured product according to the present invention has an Abbe numberof preferably 40 or more, and more preferably 50 or more.

The cured product according to the present invention has a glasstransition temperature (Tg) of preferably 100° C. or higher (e.g., 100°C. to 200° C.), and more preferably 140° C. or higher. The curedproduct, if having a glass transition temperature of lower than 100° C.,may have insufficient heat resistance in some usage modes. The glasstransition temperature of the cured product may be measured typically bythermal analyses typically using a DSC (differential scanningcalorimeter) or a TMA (thermomechanical analyzer), or by dynamicviscoelastic measurement. More specifically, the glass transitiontemperature may be measured by the measurement method described in theworking examples.

The cured product according to the present invention has a linearexpansion coefficient α1 of preferably 40 to 100 ppm/° C., and morepreferably 40 to 90 ppm/° C. at temperatures equal to or lower than theglass transition temperature. The cured product according to the presentinvention has a linear expansion coefficient α2 of preferably 90 to 150ppm/° C., and more preferably 90 to 140 ppm/° C. at temperatures equalto or higher than the glass transition temperature. The linear expansioncoefficients α1 and α2 of the cured product may be measured typicallyusing a TMA and, more specifically, may be measured by the measurementmethod described in the working examples.

The cured product according to the present invention has a storagemodulus of preferably 0.1 GPa or more, and more preferably 1 GPa ormore, at 25° C. The storage modulus of the cured product at 25° C. maybe measured typically by the dynamic viscoelastic measurement and, morespecifically, may be measured by the measurement method described in theworking examples.

The cured product according to the present invention has excellent heatresistance. After subjected to three successive heat tests based on thereflow temperature profile (highest temperature: 270° C.) described inJEDEC Standards, the cured product has a transmittance at 400 nm ofpreferably 70% or more (e.g., 70% to 100%), more preferably 75% or more,furthermore preferably 80% or more, and particularly preferably 85% ormore in terms of 0.5 mm thickness, and has a rate of yellowing ofpreferably 10% or less, and more preferably 5% or less. Thetransmittance and the rate of yellowing of the cured product may bemeasured by the measurement methods described in the working examples.

Lens Production Method

The method according to the present invention for lens productionincludes steps 1 and 2 as follows.

In the step 1, the curable composition for lens formation is chargedinto a lens-forming mold.

In the step 2, light is applied to the curable composition to cure thecurable composition.

The lens-forming mold for use in molding is not limited in material, maybe made of any of materials such as metals, glass, plastics, andsilicon, but is preferably a silicon mold among them. The productionmethod according to the present invention employs the curablecomposition for lens formation, where the curable composition hasexcellent wettability with the mold. This configuration restrains theoccurrence of “bubble entrapment” upon charging of the curablecomposition into the mold and enables the production of a lens withexcellent transfer accuracy.

The charging of the curable composition for lens formation into thelens-forming mold may be performed by a technique such as cast moldingor injection molding. The charging in the step 1, when using castmolding, may be performed by bringing the curable composition accordingto the present invention into contact with the lens-forming mold. Thecharging in the step 1, when using injection molding, may be performedby injecting the curable composition according to the present inventioninto the lens-forming mold.

As the lens-forming mold in the step 1, the use of a mold forwafer-level lens molding gives a wafer-level lens, and the use of a moldfor Fresnel lens molding gives a Fresnel lens. The production methodaccording to the present invention employs the curable composition forlens formation having excellent wettability with a mold and enables theproduction of a lens with excellent transfer accuracy even when the moldfor use herein is a mold for molding of wafer-level lenses and otherlenses reduced in size, weight, and/or thickness or for molding ofFresnel lenses and other specially-shaped lenses.

The light application in the step 2 may be performed using a lightsource within such a range that the cumulative dose is typically 500 to5000 mJ/cm². Non-limiting examples of the light source include mercurylamps, xenon lamps, carbon arc lamps, metal halide lamps, sunlight,electron beam sources, laser sources, and LED light sources. In thepresent invention, the use of a single-wavelength light source such asan LED light source (e.g., a UV-LED at a wavelength of 350 to 450 nm)enables the production of a lens that has high transparency andexcellent optical properties.

The step 2 may further include annealing after the light application.The annealing may be performed typically by heating at a temperature ofabout 100° C. to about 200° C. for about 30 minutes to 1 hour. Theannealing may be performed after demolding the workpiece from thelens-forming mold, or without demolding. The cured product of thecurable composition according to the present invention has excellentheat resistance and satisfactorily retains its shape even in ahigh-temperature environment at a temperature of about 100° C. to about200° C. Thus, the workpiece, even when being annealed after demoldingfrom the lens-forming mold, does not approximately suffer fromdeviations in lens pitch, and this enables efficient production oflenses having excellent lens center alignment accuracy.

Assume that the step 1 is performed according to a simultaneous moldingtechnique, in which a lens-forming mold having two or more lens patternsis used as the lens-forming mold. In this case, the workpiece after thestep 1 is subjected to the step 2 to give a coupled lens assemblyincluding two or more lenses coupled to each other. In this case, theresulting coupled lens assembly is cut, from which margins areeliminated as needed, to give lenses.

The lens patterns in the lens-forming mold having two or more lenspatterns may be arranged (aligned) regularly or may be disposed atrandom.

The cutting of the coupled lens assembly may be performed typically by aknown or common processing procedure. The coupled lens assembly may becut one by one, or may be cut as a laminate including two or morecoupled lens assemblies as stacked. The lens obtained by the lensproduction method according to the present invention has excellenttransfer accuracy from the mold. Thus, when two or more plies of thecoupled lens assembly are stacked and are cut while cutting linepositions are determined based on the uppermost coupled lens assembly,multiple lenses can be separated without failure (breakage). Thisenables cost reduction and working efficiency enhancement.

Non-limiting examples of the lens according to the present inventionproduced by the production method include wafer-level lenses, Fresnellenses, lenses for camera flash, and coupled lens assemblies eachincluding two or more of these lenses coupled to each other, as well aslens stacks. The term “lens stack” refers to a multilayer lens assemblyincluding two or more (e.g., two to five, and in particular two orthree) plies of the lens, or refers to a multilayer coupled lensassembly including two or more (e.g., two to five, and in particular twoor three) plies of the coupled lens assembly.

The lens stack may be produced by known or common methods. For example,the lens stack may be produced by stacking cut lenses. Alternatively,the lens stack may be produced by staking two or more coupled lensassemblies including at least one ply of the coupled lens assemblyproduced by the simultaneous molding technique to give a multilayercoupled lens assembly (laminate of coupled lens assemblies), and cuttingthe multilayer coupled lens assembly. The individual layers in the lensstack according to the present invention may be bonded or joined to eachother via a known or common bonding means, or not. The stacking of twoor more lenses gives a dramatically increased number of pixels.

The lens according to the present invention has excellent heatresistance and excellent optical properties, can satisfactorily retainits shape, and can maintain excellent optical properties even exposed toa high-temperature environment, as described on the cured productaccording to the present invention. Thus, the lens is preferably usabletypically as imaging lenses in cameras in various optical devices,spectacle lenses, light-beam condenser lenses, and light-diffusinglenses. Non-limiting examples of the cameras include car-mountedcameras, digital cameras, cameras for personal computers, cameras forcellular phones, and security cameras. The optical devices, whichinclude (are equipped with) the lens according to the present inventionor the lens stack including the lens according to the present inventionas a constitutional element, have high quality.

The lens according to the present invention can be mounted to a circuitboard by a solder reflow process. A camera module including the lensaccording to the present invention can be very efficiently mounteddirectly onto a printed circuit board (PCB) typically of a cellularphone by the same solder reflow process as with surface mounting ofother electronic components. This enables extremely efficient productionof the optical devices.

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples below. It should be noted, however, thatthe examples are by no means intended to limit the scope of the presentinvention.

Preparation Example 1: Preparation of Cycloaliphatic Epoxide (a-1)

A dehydration catalyst was prepared by mixing and stirring 70 g (0.68mol) of 95% by weight sulfuric acid and 55 g (0.36 mol) of1,8-diazabicyclo[5.4.0]undeconc-7 (DBU).

Into a 3-liter flask, 1000 g (5.05 mol) of hydrogenated biphenol (i.e.,4,4′-dihydroxybicyclohexyl), 125 g (0.68 mol in terms of sulfuric acid)of the above-prepared dehydration catalyst, and 1500 g of pseudocumene,followed by heating of the flask, where the flask was equipped with astirrer, a thermometer, and a distillation pipe equipped with adehydration tube and thermally insulated. Water production was observedaround at the time point when the internal temperature exceeded 115° C.The temperature rise was continued up to the boiling point ofpseudocumene (to an internal temperature of 162° C. to 170° C.), and adehydration reaction was performed under normal atmospheric pressure.The by-produced water was distilled and discharged via the dehydrationtube out of the system. The dehydration catalyst was liquid under thereaction conditions and was finely dispersed in the reaction mixture.Approximately an stoichiometric amount of water (180 g) was distilledafter a lapse of 3 hours, and this was defined as reaction completion.The reaction mixture after reaction completion was subjected todistillation using an Oldershaw distilling column including 10 plates todistill off pseudocumene, was further subjected to distillation at aninternal temperature of 137° C. to 140° C. and an internal pressure of10 Torr (1.33 kPa), and yielded 731 g of bicyclohexyl-3,3′-diene.

Into a reactor, 243 g of the prepared bicyclohexyl-3,3′-diene and 730 gof ethyl acetate were charged. The resulting mixture was combined with274 g of a 30% by weight solution (moisture content: 0.41% by weight) ofperacetic acid in ethyl acetate, where the solution was added dropwiseover about 3 hours while blowing nitrogen into the gas phase portion andcontrolling the temperature in the reaction system at 37.5° C. After thecompletion of dropwise addition, the mixture was aged at 40° C. for 1hour, and the reaction was completed. Further, the crude mixtureobtained upon reaction completion was washed with water at 30° C., fromwhich low-boiling compounds were removed at 70° C. and 20 mmHg, andyielded 270 g of a cycloaliphatic epoxide. The prepared cycloaliphaticepoxide had an oxirane oxygen content of 15.0% by weight. Thecycloaliphatic epoxide was also subjected to ¹H-NMR measurement to findthat a peak at a δ of about 4.5 to about 5 ppm assigned to an internaldouble bond disappeared, but a peak at a δ of about 3.1 ppm assigned toan epoxy-derived proton appeared. Thus, the prepared cycloaliphaticepoxide was identified as (3,4,3′,4′-diepoxy)bicyclohexyl.

Preparation Example 2: Preparation of Cycloaliphatic Epoxide (a-2)

Into a 5-L reactor, sodium hydroxide (granular) (499 g, 12.48 mol) andtoluene (727 mL) were charged. After nitrogen purging, the resultingmixture was combined with a solution of tetrahydrobenzyl alcohol (420 g,3.74 mol) in toluene (484 mL), followed by aging at 70° C. for 1.5hours. Next, the mixture was further combined with tetrahydrobenzylmethanesulfonate (419 g, 2.20 mol), aged under reflux for 3 hours,cooled down to room temperature, and combined with water (1248 g) toquench the reaction. An organic layer was separated, concentrated,subjected to distillation under reduced pressure, and yieldedditetrahydrobenzyl ether as a colorless, transparent liquid in a yieldof 85%. The prepared ditetrahydrobenzyl ether was subjected to ¹H-NMRspectrum measurement.

¹H-NMR (CDCl₃): δ 1.23-1.33 (m, 2H), 1.68-1.94 (m, 6H), 2.02-2.15 (m,6H), 3.26-3.34 (m, 4H), 5.63-7.70 (m, 4H)

The prepared ditetrahydrobenzyl ether (200 g, 0.97 mol), 20% SP-D(acetic acid solution) (0.39 g), and ethyl acetate (669 mL) were chargedinto a reactor, followed by temperature rise up to 40° C. Next, theresulting mixture was combined with 29.1% peracetic acid (608 g) addeddropwise over 5 hours, followed by aging for 3 hours. The resultingorganic layer was washed with an alkaline aqueous solution three timesand with ion-exchanged water two times, subjected to distillation underreduced pressure, and yielded bis(3,4-epoxycyclohexylmethyl) ether as acolorless, transparent liquid in a yield of 77%.

Preparation Example 3: Preparation of Cycloaliphatic Epoxide (a-3)

In a 1-liter jacketed flask equipped with a stirrer, a condenser, athermometer, and a nitrogen inlet tube, 36 g of water, 12.0 g of sodiumhydrogensulfate, 500 g of isopropylidene-4,4′-dicyclohexanol (suppliedby Sigma-Aldrich), and 500 g of Solvesso 150 (supplied by Exxon MobileCorporation) as a solvent were placed, followed by a dehydrationreaction at 100° C. The reaction was completed at the time point whenwater was ceased to be distilled. The reaction mixture was analyzed bygas chromatography to find that 2,2-bis(3-cyclohexen-1-yl)propane wasformed in a yield of 96%. The reaction mixture was washed with 500 ml ofion-exchanged water using a separatory funnel, of which the organiclayer was subjected to distillation under reduced pressure, and yielded387.0 g of 2,2-bis(3-cyclohexen-1-yl)propane as a colorless, transparentliquid with a purity of 96.1%.

Into a 1-liter jacketed flask as above, 100 g of the prepared2,2-bis(3-cyclohexen-1-yl)propane and 30 g of ethyl acetate werecharged. The resulting mixture was combined with 307.2 g of anapproximately anhydrous solution (having a peracetic acid concentrationof 29.1% and a moisture content of 0.47%) of peracetic acid in ethylacetate added dropwise over about 2 hours in such a manner that thetemperature in the reaction system was kept at 30° C., while blowingnitrogen into the gas phase portion. After the completion of dropwiseaddition, the mixture was aged at 30° C. for 3 hours, and the reactionwas completed. Further, the reaction mixture obtained upon reactioncompletion was washed with water at 30° C., from which low-boilingcomponents were removed at 70° C. and 20 mmHg, and yielded 99.4 g of2,2-bis(3,4-epoxycyclohex-1-yl)propane. The prepared product had, asproperties, an oxirane oxygen content of 11.3% and a viscosity of 3550cP (25° C.). The ¹H-NMR spectrum of the product demonstrated that a peakat a δ of about 4.5 to about 5 ppm assigned to an internal double bonddisappeared, but a peak at a δ of about 2.9 to about 3.1 ppm assigned toan epoxy-derived proton appeared.

Examples 1 to 8 and Comparative Examples 1 to 3

Components as given in Table 1 below were blended according to theformulations (in part by weight), stirred and mixed at room temperatureusing a planetary centrifugal mixer, and yielded uniform, transparentcurable compositions for lens formation.

TABLE 1 Comparative Examples Examples 1 2 3 4 5 6 7 8 1 2 3 CationicallyCycloaliphatic epoxide (A) (a-1) 40 30 30 30 35 30 40 40 curable (a-2)30 compound (a-3) 30 Siloxane compound (D) (d-1) 25 20 20 20 20 20 25 2030 25 25 Other cationically curable YX8000 35 35 35 35 35 35 35 35 50 3535 compound (E) OXT-221 15 15 15 15 15 15 20 OXT-101 5 Cationicphotoinitiator (B) CPI-101A 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.450.45 b-1 0.5 Leveling agent BYK-UV3510 0.5 0.5 0.5 1 0.5 0.5 BYK-307 0.50.5 0.5 F477 0.5 Other additives IN1010 1 1 1 1 1 1 1 1 1 1 1 HP-10 1 11 1 1 1 1 1 1 1 1

The abbreviations in Table 1 will be described. Cationically CurableCompounds

Cycloaliphatic Epoxides (A)

a-1: the compound prepared in Preparation Example 1((3,4,3′,4′-diepoxy)bicyclohexyl)

a-2: the compound prepared in Preparation Example 2(bis(3,4-epoxycyclohexylmethyl) ether)

a-3: the compound prepared in Preparation Example 3(2,2-bis(3,4-epoxycyclohex-1-yl)propane)

Siloxane Compounds (D)

d-1: the cyclic siloxane represented by Formula (d-1) below (trade nameX-40-2670, supplied by Shin-Etsu Chemical Co., Ltd., epoxy equivalent:200)

Other Cationically Curable Compounds (E)

YX8000: a non-ester hydrogenated bisphenol diglycidyl compound (tradename YX8000, supplied by Mitsubishi Chemical Corporation)

OXT-221: 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane (tradename ARON OXETANE OXT221, supplied by Toagosei Co., Ltd.)

OXT-101: 3-ethyl-3-hydroxymethyloxetane (trade name ARON OXETANE OXT101,supplied by Toagosei Co., Lt.)

Cationic-Polymerization Initiators (B)

CPI-101A: an aromatic sulfonium salt(4-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate, trade nameCPI-101A, supplied by San-Apro Ltd.)

b-1: 4-(phenylthio)phenyldiphenylsulfoniumphenyltris(pentafluorophenyl)borate

Leveling Agents

Polysiloxanes (C)

BYK-UV3510: a mixture of a polyether-modified polydimethylsiloxane and apolyether, trade name BYK-UV3510, supplied by BYK Japan KK

BYK-307: a mixture of a polyether-modified polydimethylsiloxane and apolyether, trade name BYK-307, supplied by BYK Japan KK

Fluorine-Containing Leveling Agents

F477: an oligomer containing a fluorine-containing group, a hydrophilicgroup, and a lipophilic group, trade name Megafac F477, supplied by DICCorporation

Antioxidants

IN1010: pentaerythritoltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenol)propionate], trade name IRGANOX 1010, supplied by BASF SE

HP-10: 2,2′-methylenebis(4,6-di-t-butylphenyl)octyl phosphite, tradename HP-10, supplied by ADEKA CORPORATION

The curable compositions for lens formation prepared in the examples andthe comparative examples were subjected to evaluations as follows.

Wettability with Mold

Viscosity

The viscosity (mPa·s) of each of the curable compositions for lensformation prepared in the examples and the comparative examples wasmeasured using a rheometer (trade name MCR301, supplied by Anton PaarJapan K.K.) at a temperature of 25° C. and a rotation speed of 20revolutions per second.

Contact Angle

Each of the curable compositions for lens formation prepared in theexamples and the comparative examples was set in a contact angle meter(trade name Dropmaster 700, supplied by Kyowa Interface Science Co.,Ltd.), 4 to 5 μL of the curable composition was dropped onto a flatsilicon substrate, and a contact angle (in degree (°)) was measured oneminute later by the sessile drop method. The silicon substrate usedherein was one prepared by curing trade name KE-1606 (supplied byShin-Etsu Chemical Co., Ltd.) at 40° C. for 6 hours and heating theresulting article at 150° C. for 30 minutes.

Number of Bubbles

There was prepared a silicon mold for a Fresnel lens illustrated inFIG. 1. The target Fresnel lens had a diameter of 4 mm and an intervalbetween the top of peaks 1 and the bottom of valleys 2 in FIG. 1(a) of300 μm. Each of the curable compositions for lens formation prepared inthe examples and the comparative examples was applied to the siliconmold and was irradiated with, and cured by, light at an irradiationintensity of 50 to 100 mW/cm and a cumulative dose of 2500 to 5000mJ/cm² using an ultraviolet irradiator (trade name ZUV-C20H, supplied byOMRON Corporation). The sample after curing was observed with a CCDcamera to count bubbles in the valleys 2 (FIG. 1(a)). The silicon moldused herein was one prepared by curing trade name KE-1606 (supplied byShin-Etsu Chemical Co., Ltd.) at 40° C. for 6 hours and heating theresulting article at 150° C. for 30 minutes.

Curability

Each of the curable compositions for lens formation prepared in theexamples and the comparative examples was evaluated on reaction rate(curability) by measuring viscoelastic behavior upon ultravioletirradiation. The measurement was performed using a viscoelasticitymeasuring apparatus (rheometer) (trade name MCR301, supplied by AntonPaar Japan K.K.) and an ultraviolet irradiator (trade name LC8, suppliedby Hamamatsu Photonics K.K.). Specifically, the time (in second) elapsedafter the ultraviolet irradiation start (the time from the ultravioletirradiation start and before the storage modulus reached 1×10⁴ Pa) wasmeasured, while the point at which the storage modulus reached 1×10⁴ Pawas taken as an index for the gel point. The analysis with the rheometerwas performed under conditions as follows:

Measurement Mode: oscillating mode

Measurement Plate Shape: parallel (12 mm in diameter)

Measurement Temperature: 25° C.

Measurement Frequency: 1 Hz

Measurement Strain: 0.1%

Each of the curable compositions for lens formation prepared in theexamples and the comparative examples was cured by an ultravioletirradiation method as follows and yielded a cured product.

Ultraviolet Irradiation Method

The curable composition for lens formation was applied to one of a pairof molds at 25° C., and a spacer having a predetermined thickness (0.5mm) was then held between the pair of molds, followed by ultravioletirradiation at an irradiation intensity of 50 to 100 mW/cm and acumulative dose of 2500 to 5000 mJ/cm² using an UV irradiator (tradename 365 nm LED Unit, supplied by Ushio Inc.).

The resulting article was demolded from the molds, heated in an oven for30 minutes to be annealed, where the oven had been preheated to 150° C.,and yielded cured products (five cured products for each curablecomposition).

The cured products of the curable compositions for lens formationprepared in the examples and the comparative examples were evaluated asfollows.

Mechanical Properties

Glass Transition Temperature: Tg

The glass transition temperature of each of the cured products of thecurable compositions for lens formation prepared in the examples and thecomparative examples was measured using a differential scanningcalorimeter (trade name Q2000, supplied by TA Instruments) in thefollowing manner. Specifically, the cured product was subjected to apretreatment in which the temperature was raised from −50° C. up to 250°C. at a rate of 20° C./min and subsequently lowered from 250° C. down to−50° C. at a rate of −20° C./min. The glass transition temperature ofthe cured product after the pretreatment was measured in a nitrogenstream at measurement temperatures in the range of −50° C. to 250° C. ata rate of temperature rise of 20° C./min.

Linear Expansion Coefficient

The linear expansion coefficients of each of the cured products of thecurable compositions for lens formation prepared in the examples and thecomparative examples were determined in the following manner. Thecoefficients of thermal expansion were measured at measurementtemperatures in the range of 30° C. to 250° C. at a rate of temperaturerise of 5° C./min using a thermomechanical analyzer (TMA) (trade nameTMA/SS100, supplied by SII NanoTechnology Inc.). A slope at a lowtemperature side was defined as a linear expansion coefficient. A linearexpansion coefficient (ppm/° C.) at temperatures equal to or lower thanthe glass transition temperature was defined as the linear expansioncoefficient α1. A linear expansion coefficient (ppm/° C.) attemperatures equal to or higher than the glass transition temperaturewas defined as the linear expansion coefficient α2.

Storage Modulus

The storage modulus (GPa) at 25° C. of each of the cured products of thecurable compositions for lens formation prepared in the examples and thecomparative examples was measured by a dynamic viscoelastic measurementmethod in conformity with JIS K 7224-1 to JIS K 7224-7, undermeasurement conditions as follows.

Measuring Apparatus: solids viscoelasticity analyzer (RSA-III, suppliedby TA Instruments)

Atmosphere: nitrogen

Temperature Range: −30° C. to 270° C.

Rate of Temperature Rise: 5° C./min

Optical Properties

Transmittance

The transmittance (transmittance before heat tests) of each of the curedproducts of the curable compositions for lens formation prepared in theexamples and the comparative examples was measured.

Specifically, the light transmittance at 400 nm was measured using aspectrophotometer (trade name U-3900, supplied by HitachiHigh-Technologies Corporation).

Refractive Index

The refractive index of each of the cured products of the curablecompositions for lens formation prepared in the examples and thecomparative examples was measured with respect to light at a wavelengthof 589 nm. The measurement was performed at 25° C. by a method inconformity with JIS K 7142, using a refractometer (trade name Model2010, supplied by Metricon Corporation).

Abbe Number

The Abbe number of each of the cured products of the curablecompositions for lens formation prepared in the examples and thecomparative examples was determined by calculation according to theequation:Abbe number=(nd−1)/(nf−nc)where nd represents a refractive index with respect to light at awavelength of 589.2 nm; of represents a refractive index with respect tolight at a wavelength of 486.1 nm; and nc represents a refractive indexwith respect to light at a wavelength of 656.3 nm. The refractiveindices were refractive indices with respect to light at thewavelengths, as measured by the method mentioned above.

Rate of Yellowing

Each of the cured products of the curable compositions for lensformation prepared in the examples and the comparative examples wassubjected to three successive heat tests based on the reflow temperatureprofile (highest temperature: 270° C.) described in JEDEC Standards,using a table-top reflow oven supplied by SHINAPEX CO., LTD. Thereafterthe light transmittance at 400 nm (transmittance after heat tests) wasmeasured by the above-mentioned method, based on which the rate ofyellowing (%) was calculated according to the equation:Rate of yellowing (%)={(Transmittance before heat tests)−(Transmittanceafter heat tests)}/(Transmittance before heat tests)×100

Results of the evaluations are summarized in Table 2.

TABLE 2 Examples Evaluation points 1 2 3 4 5 6 Wettability Viscosity(mPa · s) 395 220 223 280 390 225 with mold Contact angle (degree) 35 2534 26 30 21 Number of bubbles 0 0 0 0 0 0 Curability Time (sec) elapsedbefore storage 30 15 16 15 16 17 modulus reached 1 × 10⁴ Pa MechanicalTg 159 140 145 117 116 141 properties Linear expansion coefficient α1 8678 80 80 83 82 Linear expansion coefficient α2 125 125 119 117 122 123Storage modulus (GPa) 2.3 2.2 2.3 2.0 2.2 2.2 Cured resin Transmittance(%) at 400 nm 90.0 90.6 90.1 89.4 89.2 90.4 before heat Refractive index1.5146 1.5102 1.5093 1.5075 1.5083 1.5098 tests Abbe number 56 57 56 5655 56 Cured resin Transmittance (%) at 400 nm 89.7 90.5 90.0 89.3 89.090.3 after heat Rate of yellowing (%) 0.3 0.1 0.1 0.1 0.2 0.1 testsExamples Comparative Examples Evaluation points 7 8 1 2 3 WettabilityViscosity (mPa · s) 282 210 526 221 218 with mold Contact angle (degree)27 25 40 45 50 Number of bubbles 0 0 10 7 10 Curability Time (sec)elapsed before storage 20 16 30 17 18 modulus reached 1 × 10⁴ PaMechanical Tg 149 150-160 89 140 150 properties Linear expansioncoefficient α1 87 90 98 80 79 Linear expansion coefficient α2 128 134176 124 121 Storage modulus (GPa) 2.2 2.0 2.0 2.3 2.3 Cured resinTransmittance (%) at 400 nm 90.7 90.2 89.9 89.5 89.1 before heatRefractive index 1.5131 1.5164 1.5057 1.5139 1.5148 tests Abbe number 5657 56 56 56 Cured resin Transmittance (%) at 400 nm 90.5 88.4 89.5 89.489.1 after heat Rate of yellowing (%) 0.2 1.8 0.4 0.1 0.0 tests

INDUSTRIAL APPLICABILITY

The curable composition according to the present invention for lensformation has excellent wettability with a mold. This eliminates orminimizes the occurrence of “bubble entrapment” upon charging of thecurable composition into the mold. In addition, the curable compositionhas excellent curability and can give a cured product that has heatresistance and optical properties at excellent levels. The use of thecurable composition according to the present invention for lensformation gives a lens that has excellent transfer accuracy from themold and offers heat resistance and optical properties at excellentlevels. Thus, the curable composition is advantageously usable in usesfor the production of wafer-level lenses and other lenses reduced insize, weight, and/or thickness, and Fresnel lenses and otherspecially-shaped lenses, where the production is performed using a mold.

REFERENCE SIGNS LIST

-   -   1 peak in sawtooth cross section of Fresnel lens    -   2 valley in sawtooth cross section of Fresnel lens

The invention claimed is:
 1. A curable composition for lens formation,the curable composition comprising: a cycloaliphatic epoxide (A) beingat least one compound selected from the group consisting of(3,4,3′,4′-diepoxy)bicyclohexyl, bis(3,4-epoxycyclohexylmethyl)ether,1,2-epoxy-1,2-bis(3,4-epoxycyclohex-1-yl)ethane,2,2-bis(3,4-epoxycyclohex-1-yl)propane, and1,2-bis(3,4-epoxycyclohex-1-yl)ethane; a cationic-polymerizationinitiator (B); a polysiloxane (C) represented by Formula (c), a siloxanecompound (D) being at least one selected from the group consisting ofcompounds represented by Formulae (d-1) to (d-7), and an oxetanecompound; the curable composition containing the cycloaliphatic epoxide(A) in a content of 20% to 40% by weight, the polysiloxane (C) in anamount of 0.01% to 5% by weight, and the oxetane compound in a contentof 5% to 30% by weight, each based on the total amount of allcationically curable compounds, Formulae (c) and (d-1) to (d-7)expressed as follows:

wherein: R¹⁹ to R²² each represent, identically or differently in eachoccurrence, a group selected from hydrogen, alkyl, haloalkyl, aryl,aralkyl, alkoxy, acyloxy, and —RNHCOR′, where R is selected fromalkylene and alkenylene, and R′ is selected from alkyl and alkenyl; andm and n each represent, identically or differently, an integer of 1 ormore,

excluding a curable composition comprising compounds that contain one ormore epoxy groups per molecule other than the cycloaliphatic epoxide(A), the siloxane compound (D), and a compound containing one or moreglycidyl ether groups per molecule.
 2. The curable composition accordingto claim 1 for lens formation, further comprising a cationically curablecompound containing one or more glycidyl ether groups per molecule,excluding compounds belonging to the cycloaliphatic epoxide (A) and thesiloxane compound (D).
 3. A method of forming a wafer-level lens,comprising: curing the curable composition according to claim 1 to formthe wafer-level lens.
 4. A method of forming a Fresnel lens, comprising:curing the curable composition according to claim 1 to form the Fresnellens.
 5. A method of forming a lens for camera flash, comprising: curingthe curable composition according to claim 1 to form the lens for cameraflash.